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In a small bowl, combine 1/4 cup flour with brown sugar, cinnamon and 2 tablespoons butter.
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Cut in butter until mixture is crumbly.
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Set aside.
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Melt remaining 1/4 cup butter.
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Preheat oven to 400°F.
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Generously grease 12 muffin cups or line with papers.
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In a large mixing bowl, combine remaining 2 cups flour with sugar, baking powder, baking soda, and salt.
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Whisk to blend.
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In a separate bowl, whisk together orange juice, egg, and melted butter.
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Stir in orange zest.
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Make a well in the dry ingredients and pour in egg mixture.
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Blend with a wooden spoon until a moist, lumpy batter is formed.
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Stir in walnuts.
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Spoon into prepared muffin cups.
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Sprinkle on streusel mixture.
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Bake for 20 to 25 minutes, or until a wooden pick inserted in center comes out clean.
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Cool on a rack for 5 minutes then transfer to the rack to completely cool.